The invention relates to an integrated semiconductor mixer, having a substrate, a radio-frequency balun disposed on the substrate, a local oscillator balun disposed on the substrate, an intermediate-frequency port disposed on the substrate, and a mixer array, disposed on the substrate, that communicates with the radio-frequency balun, the local oscillator balun, and the intermediate-frequency port.
Mixers of this generic type are used in radio receivers, for instance. They can be embodied as monolithic integrated microwave circuits, using microstrip technology, so that the mixer function can be made available in a very space-saving way.
Mixers can be used as upward converters and as downward converters. When mixers are used as downward converters, a signal at a high frequency (radio frequency or RF) can be converted into a signal at a lower frequency (intermediate frequency or IF). Upward converters convert an intermediate-frequency signal into a radio-frequency signal. Downward converters generate an intermediate-frequency signal by mixing the radio-frequency signal with the signal of a local oscillator (or LO). Upward converters generate the radio-frequency signal by mixing the intermediate-frequency signal with the local oscillator signal.
It is known that mixing the signals having the various frequencies leads to the formation of addition and subtraction frequencies. For instance, the intermediate frequency, as a subtraction frequency, can represent the outcome of the mixing process, which can be processed in further circuits.
Because of the short wavelength of microwaves, a microwave mixer can be embodied in a simple way on a monolithic chip with integrated circuits. For instance, it is known to embody mixers on GaAs semiconductor substrates, but integrating the mixers with further components in order to form complete upward converters and downward converters creates the necessity of shifting over to smaller and smaller mixer arrays.
A problematic aspect of component miniaturization, however, is that the various signals carried on the same substrate influence one another. For instance, there is an influence between the signals carried by the radio-frequency balun and the signal carried by the local oscillator balun. These signals of the various baluns can also influence the operation of the mixer diodes.